What Should You Know About Flooded Steam Boilers?

Steam boilers rely on both adequate water and pressure levels. The internal vessel on your boiler has both water and air inside. The air acts as expansion space, providing the steam somewhere to go as you heat the water. When your boiler turns on, the vapor displaces the air as it travels through the system to your radiators.

If you look at your boiler, you should see a tube filled with water somewhere outside the unit. This tube is your sight glass, and it allows you to see the water level inside the tank. A water level inside the sight gauge above the max level marker indicates a flooded condition, which can significantly affect your boiler's operation and its ability to heat your home.

Why Is Flooding a Problem?

A boiler with too much water inside will operate inefficiently and produce "wet" steam. Depending on your boiler model and safety equipment, this may also trigger a shutoff and cause the boiler to stop operating. If the boiler does operate, wet steam can flush more sediment through the system, potentially causing problems with your steam plumbing or radiators.

Additionally, incorrect water levels can result in too much pressure in the boiler, damaging internal components, or potentially creating safety issues. In extreme cases, you may find that your boiler leaks water from the pressure release valve or that you need to drain the boiler repeatedly. Even without these symptoms, you generally shouldn't attempt to operate a boiler with high water levels.

What Can Cause Flooding?

Flooding can have numerous causes ranging in severity from relatively minor to more substantial. In many cases, high water levels may result from failures in the safety systems designed to maintain an appropriate water level within the vessel. These systems include automatic feeder valves and low-water cutoff switches.

A failing automatic feeder valve or one with incorrect settings may add water to the system unnecessarily, for example. This situation can create a cycle of overfilling since the wet steam will cause the apparent water level to drop as water makes its way into the pipes. A problematic low water cutoff switch can create a similar situation by incorrectly detecting a low water condition.

Other potential problems can be related to internal conditions in the boiler, including overheating (commonly referred to as "overfiring") or contamination causing variable water levels. These conditions can trigger the automatic feeder, ultimately causing the system to overfill and flood. Problems such as this can cause issues beyond flooding, so it's crucial to address them as soon as possible.

A flooded boiler may behave erratically, fail to keep your home warm, or even create safety issues. If you notice the water level in your sight glass sitting substantially above the boiler gauge line, you should contact a boiler repair technician as soon as possible to investigate the problem.